With modern materials and advanced fabrication methods, the use of corrugated materials in structures, mechanical devices and vehicles including aircraft is increasing. Corrugated shear webs, including “sine wave or arc-wave” webs in spars or beams have structural benefits over flat webs. Corrugated shear webs are naturally more stable and do not attract beam bending loads like a flat web. Weight savings by utilizing corrugated shear webs can range from 40 percent to 70 percent, depending upon the degree of post-buckling allowed in a flat web.
Corrugated materials in structures, devices, and vehicles commonly have penetrations. These penetrations typically allow electrical and hydraulic cables and lines to pass through. FIG. 1 is an example beam 2 with a corrugated web 4 and caps 5. To retain structural integrity of the web 4 when a penetration 7 is required, it is common to install a flat section of web, often called a ‘flat’ 6, within the corrugated web 4, and then install the penetration 7 in the flat 6. The flat 6 is a flat section of web without corrugations. A reinforcing ring or boss 8 is often installed and attached to the flat 6 surrounding the edges of the penetration 7, thereby reinforcing the flat 6 around the penetration 7. Typically, a flat 6 has a greater thickness, and thus a greater weight per area, than the balance of the corrugated web 4.
Prior art corrugated webs include arc webs such as the arc web 14 shown in cross-section in FIG. 2A and arc-flat webs such as the arc-flat web 16 shown in cross-section in FIG. 2B. Referring now to FIG. 2A, the arc web 14 is a linked series of alternating arcs 11 that alternate across a center plane 13. Each arc segment 11 creates a valley 12 on the concave side of the arc 11 and a peak 10 on the convex side of the arc 11. It will be appreciated that a valley 12 on one side of the web 14 is a peak 10 when viewed from the opposite side of the web 14. In this suitable example web 14, the arcs 11 have a radius 15 of 0.750 inches, and a wavelength 17 of 2.598 inches. The arcs 11 in this example transcend an arc-angle α of 120 degrees, and the interlocking arcs 11 cross the centerline or center plane 13 at an inclination angle β of 60 degrees. This exemplary arc web has an amplitude 18 of 0.75 inches.
Corrugated structural materials used for corrugated webs suitably include metals, plastics, and composite materials. In aircraft, aluminum, titanium, and fiber composite corrugated webs have been utilized.
Referring now to FIG. 2B, an arc-flat web 16 includes an alternating series of arcs 11 and straight sections 22. The straight sections 22 cross the center plane 13 at their center at an inclination of 30 degrees. Arcs 11 are alternated between planar straight sections resulting in corrugations. As in FIG. 2A, the arcs 11 result in valleys 12 at the concave side of the arcs and peaks 10, at the convex side of the arcs. In this example, the arcs 15 have a radius of 0.280 inches and the straight sections 22 between the arcs have a length of 1.120 inches. The amplitude 18 of this exemplary corrugated web is 0.635 inches centered along the center plane 13.
It will be appreciated that manufacturing a beam or other structure with a corrugated web becomes more involved when a flat, such as the flat 6 (FIG. 1), is required to be incorporated parallel to the center plane of the web to provide a reinforced landing or space for a penetration. The corrugated web may be severed and the flat attached in between corrugated sections when the beam or structure is assembled. In an arc-flat web, such as the arc-flat web 16 (FIG. 2B), for larger penetrations, it will be appreciated that an inserted flat is often substantially longer than a straight section 22. Therefore, a straight section 22 alone does not form a large enough flat to encompass the desired size penetration. Put somewhat differently, for larger penetrations, flats for penetrations often are wider than the wavelength of the corrugations, precluding the use of a part of a wavelength of a corrugation as a flat or essentially flat area to locate a penetration.
It will also be appreciated that incorporating a corrugated web with an installed flat into a beam typically includes additional or more involved fabrication steps, as compared to incorporating a continuous and uniform corrugated web in a beam. Attachment of a web with a flat to the beam caps or flanges, such as the caps 5 in the beam 2 (FIG. 1), includes transitioning the machinery or forms used to attach the webs to the caps from alternating along the corrugation to proceeding along the straight edge of the flat, and then back to alternating along the corrugation. These efforts are time-and-labor intensive and, as a result, expensive.
Therefore, an unmet need exists for improved devices and methods for reinforcing corrugated materials at penetrations.